The general goals are to study, using single unit recording and focal ablation methods in chronic trained rhesus monkeys, what the cerebellu, basal ganglia, and cerebral cortex contribute to the control of bodily movement. There are four projects, four experimental set-ups, and four investigators. A new aspect is the parallel study (noninvasive) of human (normal and cerebellar-damaged) performance of the same tasks that our monkeys perform. The first project examines cerebellar control of smooth pursuit wrist tracking of a visual target and the question of whether stretch reflexes contribute to the damping of oscillation (tremor). Damping and stiffness are measured from the oscillation that occurs after torque pulse perturbation. Tracking is against different torque motor loads which selectively increase (positive velocity feedback) and decrease (negative velocity feedback) oscillation. We will look for differences in stretch reflex EMG, spindle afferent, motor cortex and cerebellar neuronal activities as the subjects adapt to control - and not control - tremor. The second project will further examine the cerebellar role in the adaptation of the wrist to step displacements from a central held position. We will measure (1) the EMG, spindle afferent and cerebellar nuclear activity as well as that of the previously studied Purkinje cells (simple and complex spike) during 2-way adaptations (increase and decrease in displacing torque step), and (2) the performance and its adaptive capacity afterfocal cerebellar ablation. A third project, the study of pallidal neuron (1) timing (with respect to onset of movement, EMG, and cerebellar neurons) (2) coding (different relation to fast, slow, visual paced, self-paced, force vs. velocity vs. amplitude of movement, clock-like oscillatory property), and (3) ability/inability to control these parameters after pallidal lesion, will be almost or completely finished by the time this grant period would begin. The fourth project will study motor, supplementary motor, premotor, and prefrontal cortex in relation to directional signals and "set" for intended movement, individual finger movement, and combinations and sequences of movements with unit recording and focal ablation in monkeys. These experiments are designed to reveal mechanisms of (1) the contributions of these motor regions to normal movement and (2) the neurological deficits that result from the absence of these specific contributions.